This is the proposal to study the extent of gene expression in different tissues, with a special emphasis on the brain. The overall objective is to understand why the brain transcripts have an unusually large complexity compared with those of other tissues. Others have shown that in the mouse, rabbit, and human, 3 to 5 times more unique sequence DNA is transcribed into RNA in the brain than in liver, kidney, or spleen. Our research plans are: (a) to examine the complexity of the RNA in nucleus and cytoplasm of various tissues and tumor cells, with particular emphasis on neutral tissues; (b) to determine if the high level of gene expression in neural tissues is related to development and function of the nervous system; (c) to determine the relationship between nuclear and cytoplasmic RNAs in size, abundance, complexity, and rates of synthesis and degradation by using neural cell lines; (d) to examine the relationship between the complexity of nuclear RNAs and the developmental origins of different tissues. This study of transcription complements the work in our laboratory on the plasma membrane proteins of neurocells and their turmors. The major techniques used are DNA-DNA and DNA-RNA hybridizations.